The following Non-Patent Document 1 discloses a method for cutting a machining target by laser beam machining. The laser beam machining method described in the Non-Patent Document 1 aims to cut silicon wafers, and it uses light having a wavelength of about 1 μm which can transmit through silicon. The light is converged to the inside of the wafer to continuously form a modifying layer, and the wafer is cut with formation of the modifying layer as a trigger.    [Non-Patent Document 1] “LASER LIGHT DICING MACHINING IN SEMICONDUCTOR WAFER” authored by Kazunao Arai, Journal of The Society of Grinding Engineers, Vol. 47, No. 5, 2003 May. pp. 229-231.